An electric vehicle is a vehicle running by a battery power. There are several types such as a pure electric vehicle running only by electric power of a battery and a hybrid electric vehicle running by power of an internal combustion engine and electric power of a battery.
The pure electric vehicle runs only by power of a motor operating by electric power of a battery. The hybrid electric vehicle runs by efficiently combining power of the internal combustion engine and power of the motor.
For example, as illustrated in FIG. 1, a hybrid electric vehicle includes: an engine 10; a motor 20; an engine clutch 30 which controls power transmission between the engine 10 and the motor 20; a transmission 40; a differential gear 50; a battery 60; an integrated starter-generator (ISG) 70 which starts the engine 10 or generates electric power by output of the engine 10; and wheels 80.
The hybrid electric vehicle further includes: a hybrid control unit (HCU) 200 for controlling an overall operation of the hybrid electric vehicle; an engine control unit (ECU) 110 for controlling an operation of the engine 10; a motor control unit (MCU) 120 for controlling an operation of the motor 20; a transmission control unit (TCU) 140 for controlling an operation of the transmission 40; and a battery control unit (BCU) 160 for managing and controlling the battery 60.
The BCU 160 may also be referred to as a battery management system (BMS), and the ISG 70 may also be referred to as a starting/generating motor or a hybrid starter-generator (HSG).
The hybrid electric vehicle may be driven in an electric vehicle (EV) mode which is a mode of a true electric vehicle solely using power of the motor 20, a hybrid electric vehicle (HEV) mode using torque of the motor 20 as an auxiliary power while using torque of the engine 10 as a main power; and a regenerative braking (RB) mode collecting braking and inertia energy through power generation of the motor 20 to charge the battery 60 during braking or driving using the inertia of the vehicle.
The motor 20 of the hybrid electric vehicle and a motor of the pure electric vehicle generally operate as a generator for collecting inertial energy during the regenerative braking (RB) mode. The running by inertial energy of an electric vehicle such as the hybrid electric vehicle and the pure electric vehicle may refer to as coasting. When the motor operates as a generator for collecting the inertial energy, braking of the electric vehicle also occurs.
As shown in FIG. 2, by setting a negative (minus) torque to the motor while coasting, the inertia energy may be collected as a regenerative electric power, and braking of the electric vehicle may also occur.
When the motor operates as a generator, the regenerative electric power generally charges a battery and/or a high voltage battery to drive the motor of the electric vehicle.
However, when the battery is in a fully charged state such that charging is limited or in an over-temperature state, the regenerative electric power from the motor 20 cannot charge the battery. In that case, because the regenerative braking also occurring with regenerative power generation by the motor 20 cannot be performed, the electric vehicle may collide with a foregoing vehicle.
When the battery is in the fully charged state while coasting, an electric vehicle according to an exemplary embodiment of the related art performs a fuel-cut control instead of the regenerative braking and uses friction torque (negative torque) of the engine, as shown in FIG. 3.
In another exemplary embodiment of the related art, when the battery is in the fully charged state while coasting, the regenerative electric power of the motor produced by the regenerative braking is consumed by an air conditioner or a heater 90 as shown in FIG. 4.
However, according to the exemplary embodiments of the related art as described above, temperature in the electric vehicle may be varied due to the unwanted operation of the air conditioner or heater, and drivability may rapidly deteriorate due to the fuel-cut.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.